The present invention relates to a high-frequency power amplifier circuit which is used by a wireless communication system such as mobile telephones and which amplifies a high-frequency signal before outputting the amplified signal, and to an electronic part incorporating such a high-frequency power amplifier circuit. More particularly, the invention relates to a wireless communication system for varying input power of a high-frequency power amplifier circuit in order to control output power of the circuit, the output power being controlled while the gain of the high-frequency power amplifier circuit is being kept constant regardless of temperature variations.
There has been in use a wireless communication system (mobile communication apparatus) such as a mobile telephone operating on a principle called GSM (Global System for Mobile Communication) that utilizes a frequency band of 880 through 915 MHz. GSM is based on a phase modulation method called GMSK (Gaussian Minimum Shift Keying) whereby the phase of a carrier is shifted in keeping with transmitted data. In recent years, a new mobile telephone that works in at least two modes has been proposed. The proposed telephone causes voice to be modulated by GMSK for communication while allowing data to be modulated by EDGE (Enhanced Data Rates for GMS Evolution) for communication, the latter method supplementing the phase-shifting GMSK method with amplitude shifting capabilities.
A transmission output block of the wireless communication system (mobile communication apparatus) such as the mobile telephone incorporates a high-frequency power amplifier circuit (called the power amplifier circuit hereunder) for amplifying a modified signal. In conventional wireless communication systems, the gain of the power amplifier circuit is controlled in accordance with the level of transmission requests coming from a base band circuit or from a control circuit such as a micro-processor. The control is accomplished by detecting the output level of the power amplifier circuit or an antenna and by feeding what is detected back to the amplifier circuit so as to vary a bias voltage or a bias current of the circuit, whereby the gain of the power amplifier circuit is controlled. This scheme is disclosed illustratively in Japanese Published Unexamined Patent Application No. 2000-151310.